Steam valve driving apparatus

ABSTRACT

In a steam valve driving apparatus according to an embodiment, a control valve permits or blocks a flow of hydraulic oil from a supply port to an opening direction piston chamber. A dump valve blocks or permits the flow of the hydraulic oil from the opening direction piston chamber to a discharge port. A blocking valve permits or blocks a flow of the hydraulic oil from an accumulator to a closing direction piston chamber. The control valve permits the flow of control oil from the closing direction piston chamber to the discharge port in a state where the flow of hydraulic oil from the supply port to the opening direction piston chamber is permitted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/JP2019/005275, filed on Feb. 14, 2019 based upon and claims thebenefit of priority from Japanese Patent Application No. 2018-032368,filed Feb. 26, 2018; the entire contents of which are incorporatedherein by reference.

FIELD

Embodiments described herein generally relate to a steam valve drivingapparatus.

BACKGROUND

A steam valve that controls the supply of steam to a steam turbine isdriven to open and close by a steam valve driving apparatus. Such asteam valve driving apparatus needs to include not only a function forperforming speed control and load control of the turbine, but also afail-safe function for safely stopping the turbine when control is lost.In order to provide a fail-safe function, a known steam valve drivingapparatus includes a closing spring that constantly applies a biasingforce (spring force) acting as a load to a valve body of the steam valvein the closing direction of the steam valve.

A typical steam valve driving apparatus having such a closing springwill be described with reference to FIGS. 21 and 22. A cylinder 100 inthe steam valve driving apparatus illustrated in FIGS. 21 and 22includes: a piston 101; a piston chamber 102 to which control oil forpressing the piston 101 in the opening direction is supplied; and aclosing spring 103. The closing spring 103 biases the piston 101 in theclosing direction of a steam valve SV. This biasing force is constantlyapplied as a load regardless of the open/close state.

As illustrated in FIG. 21, the control oil is supplied to the pistonchamber 102 of the cylinder 100 via the servo valve 104 so that thepiston 101 is pressed in the opening direction by the control oil. Thepiston chamber 102 is connected with an A-port of a dump valve 105, withan X-port of the dump valve 105 connected to a trip solenoid valve 106.In the case of resetting the steam valve SV (opening the steam valveSV), the trip solenoid valve 106 is energized, and emergency oil issupplied to the X-port of the dump valve 105 via the trip solenoid valve106, leading to a closed state of the dump valve 105. In the case oftripping the steam valve SV (rapidly closing the steam valve SV), thetrip solenoid valve 106 is de-energized and this causes the emergencyoil in the X-port of the dump valve 105 to be discharged, as illustratedin FIG. 22. As a result, the dump valve 105 is opened, and the controloil in the piston chamber 102 is discharged via the B-port of the dumpvalve 105. Therefore, the piston 101 moves in the closing direction bythe biasing force of the closing spring 103, causing the steam valve SVto be rapidly closed.

In this manner, the control oil supplied to the piston chamber 102presses the piston 101 in the opening direction. In contrast, the piston101 is pressed in the closing direction by the closing spring 103provided in the cylinder 100, not by the control oil. The cylinder 100of such a steam valve driving apparatus is sometimes referred to as asingle-acting type because the piston 101 is driven in one direction(opening direction of the steam valve) by hydraulic pressure.

In general, increasing an output of a turbine generator joined to asteam turbine would also increase the flow rate of steam supplied to thesteam turbine. This increases the valve diameter of the steam valve andincreases the spring force required for the closing spring. In thiscase, since the biasing force of the closing spring is constantlyapplied as a load to the piston. Accordingly, in order to counter thebiasing force, the volume of the cylinder of the steam valve drivingapparatus increases, leading to enlargement of the cylinder.

In the case of rapidly closing the steam valve in an emergency, it isnecessary to rapidly discharge the control oil in the cylinder. However,as described above, there is a problem that an increase in the cylindervolume prolongs the time for discharging the control oil in thecylinder. In this case, the overspeed characteristic of the steamturbine might be deteriorated. Such a problem is considered to be causedby the fact that the biasing force of the closing spring for providingthe fail-safe function is constantly applied as a load to the piston.For this reason, it is desired to provide a steam valve drivingapparatus that would not cause the force for exerting the fail-safefunction to be applied as a load to the piston other than in emergency(that is, in a case where the steam valve is open).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system diagram illustrating a steam valve driving apparatusat the time of resetting a steam valve in a first embodiment.

FIG. 2 is a system diagram at the time of trip of the steam valve in thesteam valve driving apparatus of FIG. 1.

FIG. 3 is a system diagram illustrating a steam valve driving apparatusat the time of resetting the steam valve in a second embodiment.

FIG. 4 is a system diagram at the time of trip of the steam valve in thesteam valve driving apparatus of FIG. 3.

FIG. 5 is a system diagram illustrating a steam valve driving apparatusat the time of resetting the steam valve in a third embodiment.

FIG. 6 is a system diagram at the time of trip of the steam valve in thesteam valve driving apparatus of FIG. 5.

FIG. 7 is a system diagram illustrating a steam valve driving apparatusat the time of resetting the steam valve in a fourth embodiment.

FIG. 8 is a system diagram at the time of trip of the steam valve in thesteam valve driving apparatus of FIG. 7.

FIG. 9 is a system diagram illustrating a steam valve driving apparatusat the time of resetting the steam valve in a fifth embodiment.

FIG. 10 is a system diagram at the time of trip of the steam valve inthe steam valve driving apparatus of FIG. 9.

FIG. 11 is a system diagram illustrating a steam valve driving apparatusat the time of resetting the steam valve in a sixth embodiment.

FIG. 12 is a system diagram at the time of trip of the steam valve inthe steam valve driving apparatus of FIG. 11.

FIG. 13 is a system diagram illustrating a steam valve driving apparatusat the time of resetting the steam valve in a seventh embodiment.

FIG. 14 is a system diagram at the time of trip of the steam valve inthe steam valve driving apparatus of FIG. 13.

FIG. 15 is a system diagram illustrating a steam valve driving apparatusat the time of resetting the steam valve in an eighth embodiment.

FIG. 16 is a system diagram at the time of trip of the steam valve inthe steam valve driving apparatus of FIG. 15.

FIG. 17 is a system diagram illustrating a steam valve driving apparatusat the time of resetting the steam valve in a ninth embodiment.

FIG. 18 is a system diagram at the time of trip of the steam valve inthe steam valve driving apparatus of FIG. 17.

FIG. 19 is a system diagram illustrating a steam valve driving apparatusat the time of resetting the steam valve in a tenth embodiment.

FIG. 20 is a system diagram at the time of trip of the steam valve inthe steam valve driving apparatus of FIG. 19.

FIG. 21 is a system diagram at the time of resetting a steam valve in atypical steam valve driving apparatus.

FIG. 22 is a system diagram at the time of trip of the steam valve inthe steam valve driving apparatus of FIG. 21.

DETAILED DESCRIPTION

A steam valve driving apparatus according to an embodiment is a steamvalve driving apparatus regulating open and close position of a steamvalve. The steam valve driving apparatus includes a supply portconfigured to supply hydraulic oil, a discharge port configured todischarge hydraulic oil, and a cylinder. The cylinder includes: a pistonjoined to a steam valve; an opening direction piston chamber to whichhydraulic oil that presses the piston in the opening direction of thesteam valve is supplied; and a closing direction piston chamber to whichhydraulic oil for pressing the piston in the closing direction of thesteam valve is supplied. The steam valve driving apparatus includes acontrol valve, a dump valve, an accumulator, a blocking valve, and atrip solenoid valve. The control valve is configured to permit or blockthe flow of hydraulic oil from the supply port to the opening directionpiston chamber. The dump valve is configured to block or permit the flowof hydraulic oil from the opening direction piston chamber to thedischarge port. The accumulator is configured to store hydraulic oilunder pressure. The blocking valve is configured to permit or block theflow of hydraulic oil from the accumulator to the closing directionpiston chamber. The trip solenoid valve is configured to control thedump valve and the blocking valve. The control valve is configured topermit the flow of control oil from the closing direction piston chamberto the discharge port in a state where the flow of hydraulic oil fromthe supply port to the opening direction piston chamber is permitted.

The steam valve driving apparatus according to an embodiment is a steamvalve driving apparatus regulating open and close position of a steamvalve. The steam valve driving apparatus includes a supply portconfigured to supply hydraulic oil, a discharge port configured todischarge hydraulic oil, and a cylinder. The cylinder includes: a firstpiston joined to a steam valve; an opening direction first pistonchamber to which hydraulic oil that presses the first piston in anopening direction of the steam valve is supplied; a second pistonreleasably arranged with respect to the steam valve; an openingdirection second piston chamber to which hydraulic oil for pressing thesecond piston in a steam valve opening direction is supplied; and aclosing direction second piston chamber that presses the second pistonin a steam valve closing direction. The steam valve driving apparatusincludes a control valve, a first dump valve, a trip solenoid valve, anda second dump valve. The control valve is configured to permit or blockthe flow of hydraulic oil from the supply port to the opening directionfirst piston chamber. The first dump valve is configured to block orpermit the flow of hydraulic oil from the opening direction first pistonchamber to the discharge port. The trip solenoid valve is configured topermit or block the flow of hydraulic oil from the supply port to theopening direction second piston chamber. The second dump valve isconfigured to block or permit the flow of hydraulic oil from the openingdirection second piston chamber to the discharge port. The second pistonis joined to the steam valve in the case of closing the steam valve, andis separated from the steam valve in the case of opening the steamvalve.

Hereinafter, a steam valve driving apparatus according to embodiments ofthe present invention will be described with reference to the drawings.

First Embodiment

A steam valve driving apparatus 1 in a first embodiment will bedescribed with reference to FIGS. 1 and 2. The steam valve drivingapparatus 1 illustrated here is a hydraulic driving apparatus thatperforms opening and closing drive of a valve body VB of a steam valveSV.

As illustrated in FIG. 1, the steam valve driving apparatus 1 accordingto the present embodiment includes a cylinder 10, and a manifold block20 that supplies control oil (hydraulic oil) to the cylinder 10.

The cylinder 10 includes a piston 11 joined to the valve body VB, anopening direction piston chamber 12 to which control oil for pressingthe piston 11 in the opening direction of the valve body VB is supplied,and a closing direction piston chamber 13 to which control oil to pressthe piston 11 in the closing direction of the valve body VB is supplied.The opening direction piston chamber 12, among these, has two a-ports.It is configured such that control oil flows into the opening directionpiston chamber 12 from each of the a-ports, and control oil in theopening direction piston chamber 12 flows out from each of the a-ports.The closing direction piston chamber 13 has a b-port. It is configuredsuch that control oil flows into the closing direction piston chamber 13from the b-port, and control oil in the closing direction piston chamber13 flows out from the b-port.

The piston 11 is joined to the valve body VB via a valve rod VA, andmoves linearly in accordance with the pressure of the control oil in theopening direction piston chamber 12 and the pressure of the control oilin the closing direction piston chamber 13, so as to drive the valvebody VB. In the configuration illustrated in FIG. 1, the openingdirection of the valve body VB corresponds to an upward direction, whilethe closing direction of the valve body VB corresponds to a downwarddirection. With this configuration, when control oil is supplied to theopening direction piston chamber 12 of the cylinder 10, the piston 11moves upward under the pressure of the control oil, and moves the valvebody VB in the opening direction. In contrast, when the control oil issupplied to the closing direction piston chamber 13 of the cylinder 10,the piston 11 moves downward under the pressure of the control oil, andmoves the valve body VB in the closing direction. In this manner, thecylinder 10 according to the present embodiment is sometimes referred toas a double-acting type because the piston 11 is driven in bothdirections (opening direction and closing direction of the steam valveSV) by hydraulic pressure.

The manifold block 20 includes: a supply port 21 that supplies controloil; and a discharge port 22 that discharges control oil. The supplyport 21, among these, is connected to a control oil supply system via acontrol oil supply pipe 2, and the control oil is to be supplied to thesupply port 21 from this control oil supply system. The discharge port22 is connected to the drain system via a drain pipe 3, and the controloil discharged from the discharge port 22 is supplied to the drainsystem.

The manifold block 20 further includes a servo valve 23 (control valve),a dump valve 24, an accumulator 25, a blocking valve 26, and a tripsolenoid valve 27.

The servo valve 23 is configured to be switchable between a statepermitting the flow of the control oil from the supply port 21 to theopening direction piston chamber 12 and a state blocking the flow of thecontrol oil (to permit or block the flow of the control oil). The servovalve 23 is configured to be switchable between a state permitting theflow of control oil from the closing direction piston chamber 13 to thedischarge port 22 and a state blocking the flow of control oil (topermit or block the flow of the control oil). The servo valve 23 in thepresent embodiment has a configuration in which the flow of the controloil from the closing direction piston chamber 13 to the discharge port22 is permitted in a state where the flow of control oil from the supplyport 21 to the opening direction piston chamber 12 is permitted. Incontrast, the servo valve 23 has a configuration in which the flow ofthe control oil from the closing direction piston chamber 13 to thedischarge port 22 is blocked in a state where the flow of control oilfrom the supply port 21 to the opening direction piston chamber 12 isblocked.

More specifically, the servo valve 23 has a configuration in which theP-port of the servo valve 23 and the supply port 21 are connected by afirst control oil supply path 28 (hydraulic oil supply path). Inaddition, the A-port of the servo valve 23 and the b-port of the closingdirection piston chamber 13 are connected by a first closed-side channel29, while the B-port of the servo valve 23 and the a-port of the openingdirection piston chamber 12 are connected by an open-side channel 30. AT-port of the servo valve 23 is connected to a servo discharge path 31.The servo discharge path 31 merges a dump discharge path 41 describedbelow, and is connected to the discharge port 22 via the dump dischargepath 41.

The servo valve 23 is configured such that, when a first electricalsignal (electrical command in the opening direction) transmitted from acontrol device (not illustrated) is input to a coil, the P-port andB-port of the servo valve 23 communicate with each other, so as topermit the flow of control oil from the first control oil supply path 28to the open-side channel 30. With this configuration, the control oil issupplied from the first control oil supply path 28 to the open-sidechannel 30 via the P-port and B-port of the servo valve 23. In addition,an input of the first electrical signal causes the A-port and the T-portof the servo valve 23 to communicate with each other, so as to permitthe flow of control oil from the first closed-side channel 29 to theservo discharge path 31. With this configuration, the control oil issupplied from the first closed-side channel 29 to the servo dischargepath 31 via the A-port and T-port of the servo valve 23. The control oilsupplied to the servo discharge path 31 is then supplied to thedischarge port 22 via the dump discharge path 41, and discharged fromthe discharge port 22.

Meanwhile, when a second electrical signal (electrical command in theclosing direction) transmitted from the control device is input to acoil, the P-port and B-port of the servo valve 23 are blocked asillustrated in FIG. 2, so as to block the flow of control oil from thefirst control oil supply path 28 to the open-side channel 30. Inaddition, the A-port and the T-port are blocked, so as to block the flowof control oil from the first closed-side channel 29 to the servodischarge path 31. Instead, the P-port and the A-port communicate witheach other, allowing communication between the first control oil supplypath 28 and the first closed-side channel 29. This also allowscommunication between the B-port and the T-port, while allowingcommunication between the open-side channel 30 and the servo dischargepath 31.

As illustrated in FIG. 1, the first control oil supply path 28 isprovided with a supply port-side check valve 32 (supply port-sidebackflow prevention function valve). The supply port-side check valve 32is disposed in the first control oil supply path 28 on the side closerto the supply port 21 rather than to a branch point P2 described below.The supply port-side check valve 32 is configured to permit the flow ofcontrol oil to the servo valve 23 and block the flow of control oil tothe supply port 21. In addition, the cracking pressure of the supplyport-side check valve 32 is set to a minimum operating pressure of thesteam valve driving apparatus 1.

The open-side channel 30 is provided with a first open-side pilot checkvalve 33 (open-side backflow prevention valve). The first open-sidepilot check valve 33 is controlled by the trip solenoid valve 27.

More specifically, the first open-side pilot check valve 33 is disposedin the open-side channel 30 on the side closer to the servo valve 23rather than to a branch point P1 to which a below-described dump channel40 is connected. The A-port and B-port of the first open-side pilotcheck valve 33 form a part of the open-side channel 30. The X-port(pilot port) of the first open-side pilot check valve 33 is connectedwith the B-port of the trip solenoid valve 27. In the state whereemergency oil described below from the trip solenoid valve 27 issupplied to the X-port, the X-port would be pressurized by the emergencyoil to cause the first open-side pilot check valve 33 to lose thebackflow prevention function so as to permit the flow of control oil inboth directions. In contrast, the first open-side pilot check valve 33has a backflow prevention function in a state where emergency oil is notsupplied to the X-port (emergency oil is discharged). This would permitthe flow of the control oil to the opening direction piston chamber 12,while blocking the flow of control oil to the servo valve 23.

The open-side channel 30 is provided with a second open-side pilot checkvalve 34. The second open-side pilot check valve 34 is controlled by thetrip solenoid valve 27.

More specifically, the second open-side pilot check valve 34 is disposedin the open-side channel 30 on the side closer to the opening directionpiston chamber 12 rather than to the branch point P1 to which thebelow-described dump channel 40 is connected. The A-port and B-port ofthe second open-side pilot check valve 34 form a part of the open-sidechannel 30. The X-port (pilot port) of the second open-side pilot checkvalve 34 is connected with the B-port of the trip solenoid valve 27. Ina state where emergency oil is supplied to the X-port, the X-port wouldbe pressurized by the emergency oil to cause the second open-side pilotcheck valve 34 to lose the backflow prevention function so as to permitthe flow of control oil in both directions. In contrast, the secondopen-side pilot check valve 34 has a backflow prevention function in astate where emergency oil is not supplied to the X-port. This wouldpermit the flow of control oil to the branch point P1, while blockingthe flow of the control oil to the opening direction piston chamber 12.

Note that the open-side channel 30 branches into two channels so as tobe connected to the two a-ports of the opening direction piston chamber12 on the side closer to the opening direction piston chamber 12 ratherthan to the second open-side pilot check valve 34. Each of the channelsis provided with orifices 36 and 37, and the flow rate of each of thechannels is adjusted.

The first closed-side channel 29 is provided with a closed-side pilotcheck valve 35 (closed-side backflow prevention valve). The closed-sidepilot check valve 35 is controlled by the trip solenoid valve 27.

More specifically, the closed-side pilot check valve 35 is disposed inthe first closed-side channel 29 on the side closer to the servo valve23 rather than to a branch point P4 to which a second closed-sidechannel 44 described below is connected. The A-port and B-port of theclosed-side pilot check valve 35 form a part of the first closed-sidechannel 29. The X-port (pilot port) of the closed-side pilot check valve35 is connected with the B-port of the trip solenoid valve 27. In thestate where emergency oil is supplied to the X-port, the X-port would bepressurized by the emergency oil to cause the closed-side pilot checkvalve 35 to lose the backflow prevention function so as to permit theflow of control oil in both directions. In contrast, the closed-sidepilot check valve 35 has a backflow prevention function in a state whereemergency oil is not supplied to the X-port. This would permit the flowof control oil to the closing direction piston chamber 13, whileblocking the flow of the control oil to servo valve 23.

Note that the first closed-side channel 29 is provided with an orifice38, thereby adjusting the flow rate of the first closed-side channel 29.The orifice 38 is disposed in the first closed-side channel 29 on theside closer to the closing direction piston chamber 13 rather than tothe branch point P4 of the second closed-side channel 44 describedbelow.

The servo discharge path 31 is provided with a check valve 39. The checkvalve 39 is configured to permit the flow of control oil to thedischarge port 22 and block the flow of control oil or emergency oil tothe servo valve 23. That is, the check valve 39 prevents the control oildischarged from the A-port of the dump valve 24 or the cylinder 10, orthe emergency oil discharged from the T-port of the trip solenoid valve27, from being supplied to the T-port of the servo valve 23.

The dump valve 24 is configured to be switchable between a stateblocking the flow of control oil from the opening direction pistonchamber 12 to the discharge port 22 and a state permitting the flow ofcontrol oil (to permit or block the flow of the control oil).

More specifically, the dump valve 24 has a configuration in which theB-port of the dump valve 24 and the open-side channel 30 are connectedby the dump channel 40. The dump channel 40 is connected to the branchpoint P1 (halfway position) provided in the open-side channel 30 on theside closer to the opening direction piston chamber 12 rather than tothe first open-side pilot check valve 33. This branch point P1 isdisposed in the open-side channel 30 on the side closer to the servovalve 23 rather than to the second open-side pilot check valve 34. Thatis, the branch point P1 is disposed between the first open-side pilotcheck valve 33 and the second open-side pilot check valve 34. The A-portof the dump valve 24 is connected with the dump discharge path 41. Thedump discharge path 41 is connected to the discharge port 22. The X-port(pilot port) of the dump valve 24 is connected to the B-port of the tripsolenoid valve 27.

The dump valve 24 is controlled by the trip solenoid valve 27. That is,the dump valve 24 is configured such that, in the state where emergencyoil is supplied from the B-port to the X-port of the trip solenoid valve27, the X-port is pressurized by the emergency oil and closed, blockingthe B-port and the A-port of the dump valve 24. This blocks the flow ofcontrol oil from the opening direction piston chamber 12 to thedischarge port 22. In contrast, in a state where the emergency oil isnot supplied to the X-port, the dump valve 24 is opened, allowingcommunication between the B-port and the A-port of the dump valve 24.This permits the flow of control oil from the opening direction pistonchamber 12 to the discharge port 22, allowing the control oil to besupplied from the open-side channel 30 to the dump discharge path 41 viathe B-port and the A-port of the dump valve 24. The control oil suppliedto the dump discharge path 41 is then supplied to the discharge port 22,so as to be discharged from the discharge port 22.

The accumulator 25 stores control oil under pressure. That is, a gassuch as nitrogen is sealed in the accumulator 25, and the gas isseparated by a diaphragm (bladder type accumulator) or a piston (pistontype accumulator). Filling the control oil while compressing the gaswith this configuration enables the accumulator 25 to store thepressurized control oil. The accumulator 25 and the first control oilsupply path 28 are connected by an accumulator filling path 42. Theaccumulator filling path 42 is connected to the branch point P2 (halfwayposition) provided in the first control oil supply path 28 on the sidecloser to the servo valve 23 side rather than to the supply port-sidecheck valve 32 described above. The control oil supplied to the supplyport 21 is then supplied to the accumulator 25 via the first control oilsupply path 28 and the accumulator filling path 42, and the accumulator25 is filled with the control oil.

The blocking valve 26 is configured to be switchable between a statepermitting the flow of control oil from the accumulator 25 to theclosing direction piston chamber 13 and a state blocking the flow of thecontrol oil (to permit or block the flow of the control oil).

More specifically, the blocking valve 26 has a configuration in whichthe P-port of the blocking valve 26 and the accumulator 25 are connectedby an accumulator discharge path 43. The accumulator discharge path 43is connected to the accumulator filling path 42 at a branch point P3.The A-port of the blocking valve 26 and the first closed-side channel 29are connected by the second closed-side channel 44. The secondclosed-side channel 44 is connected to the branch point P4 (halfwayposition) provided in the first closed-side channel 29 on the sidecloser to the closing direction piston chamber 13 rather than to theclosed-side pilot check valve 35. The X-port (pilot port) of theblocking valve 26 is connected to the B-port of the trip solenoid valve27.

The blocking valve 26 is controlled by the trip solenoid valve 27. Thatis, the blocking valve 26 is configured such that, in the state whereemergency oil is supplied from the B-port of the trip solenoid valve 27to the X-port, the X-port is pressurized by the emergency oil andclosed, blocking the P-port and the A-port of the blocking valve 26.This blocks the flow of control oil from the accumulator 25 to theclosing direction piston chamber 13. In contrast, in a state where theemergency oil is not supplied to the X-port, the blocking valve 26 isopened, allowing communication between the P-port and the A-port of theblocking valve 26. This permits the flow of control oil from theaccumulator 25 to the closing direction piston chamber 13, and thecontrol oil is supplied from the accumulator discharge path 43 to thesecond closed-side channel 44 via the P-port and A-port of the blockingvalve 26. The control oil supplied to the second closed-side channel 44is then supplied to the closing direction piston chamber 13 via thefirst closed-side channel 29.

The trip solenoid valve 27 controls the dump valve 24 and the blockingvalve 26 as described above. The trip solenoid valve 27 is configured tobe switchable between a state permitting the flow of the emergency oilfrom the supply port 21 to the X-port of the dump valve 24 and theX-port of the blocking valve 26, and a state permitting the flow of theemergency oil from the X-port of the dump valve 24 and the X-port of theblocking valve 26 to the discharge port 22. The trip solenoid valve 27controls the first open-side pilot check valve 33, the second open-sidepilot check valve 34, and the closed-side pilot check valve 35. That is,in a case where the trip solenoid valve 27 permits the flow of theemergency oil to the X-port of the dump valve 24 and the X-port of theblocking valve 26, the trip solenoid valve 27 permits the flow of theemergency oil to each of the X-port of the first open-side pilot checkvalve 33, the X-port of the second open-side pilot check valve 34, andthe X-port of the closed-side pilot check valve 35. Here, emergency oilmeans the control oil (hydraulic oil) supplied from the trip solenoidvalve 27 to the X-port of each of the valves.

More specifically, the trip solenoid valve 27 has a configuration inwhich the P-port of the trip solenoid valve 27 and the first control oilsupply path 28 are connected by a second control oil supply path 45. Thesecond control oil supply path 45 is connected to the branch point P2(halfway position) provided in the first control oil supply path 28 onthe side closer to the servo valve 23 rather than to the supplyport-side check valve 32. In the configuration illustrated in FIG. 1,there is a match in the branch point at which the accumulator fillingpath 42 is connected to the first control oil supply path 28, and thebranch point at which the second control oil supply path 45 is connectedto the first control oil supply path 28. However, the present embodimentis not limited to this. The B-port of the trip solenoid valve 27 isconnected to the X-port of the dump valve 24 and the X-port of theblocking valve 26 via an emergency oil channel 46. The B-port of thetrip solenoid valve 27 is also connected to the X-port of the firstopen-side pilot check valve 33, the X-port of the second open-side pilotcheck valve 34, and the X-port of the closed-side pilot check valve 35via the emergency oil channel 46. The emergency oil channel 46 has abranch structure so as to connect the B-port of the trip solenoid valve27 to the X-ports of the valves 24, 26, 33 to 35. The T-port of the tripsolenoid valve 27 is connected to a trip discharge path 47. The tripdischarge path 47 merges with the dump discharge path 41 describedabove, and is connected to the discharge port 22 via the trip dischargepath 47.

The trip solenoid valve 27 includes a coil that is energized when itreceives an electrical signal transmitted from a control device (notillustrated). Energization of the coil allows communication between theP-port and B-port of the trip solenoid valve 27, and permits the flow ofemergency oil from the second control oil supply path 45 to theemergency oil channel 46. With this configuration, the emergency oil issupplied from the second control oil supply path 45 to the emergency oilchannel 46 via the P-port and B-port of the trip solenoid valve 27. Incontrast, in the absence of the electrical signal, the coil isde-energized and the P-port and B-port of the trip solenoid valve 27 areblocked, so as to block the flow of the emergency oil from the secondcontrol oil supply path 45 to the emergency oil channel 46. Instead, theT-port and the B-port come in communication with each other, permittingthe flow of the emergency oil from the emergency oil channel 46 to thetrip discharge path 47. With this configuration, the emergency oil issupplied from the emergency oil channel 46 to the trip discharge path 47via the B-port and T-port of the trip solenoid valve 27. The emergencyoil supplied to the trip discharge path 47 is supplied to the dischargeport 22 via the dump discharge path 41, and then discharged from thedischarge port 22.

The trip discharge path 47 is provided with a check valve 48. The checkvalve 48 is configured to permit the flow of the emergency oil to thedischarge port 22 and block the flow of the control oil to the tripsolenoid valve 27. That is, the check valve 48 prevents the control oildischarged from the T-port of the servo valve 23, discharged from theA-port of the dump valve 24, or discharged from the cylinder 10, frombeing supplied to the T-port of the trip solenoid valve 27.

Next, actions in the present embodiment having such a configuration willbe described.

In the case of opening (resetting) the steam valve SV, the trip solenoidvalve 27 is energized as illustrated in FIG. 1. This allowscommunication between the P-port and B-port of the trip solenoid valve27, so as to supply the emergency oil from the supply port 21 to theX-port of the dump valve 24 and the X-port of the blocking valve 26 viathe trip solenoid valve 27 and the emergency oil channel 46. With thisconfiguration, the X-port of the dump valve 24 is pressurized to closethe dump valve 24. This will block the flow of control oil from theopening direction piston chamber 12 to the discharge port 22. The X-portof the blocking valve 26 is also pressurized, closing the blocking valve26 as well. This blocks the flow of control oil from the accumulator 25to the closing direction piston chamber 13.

Energization of the trip solenoid valve 27 allows the emergency oil tobe also supplied to the X-port of the first open-side pilot check valve33, the X-port of the second open-side pilot check valve 34, and theX-port of the closed-side pilot check valve 35, so as to pressurize theX-port of each of the valves 33 to 35. With this pressurization, thecheck valve function of each of the valves 33 to 35 is lost, permittingthe flow of the control oil in both directions in each of the valves 33to 35.

Furthermore, in the case of opening the steam valve SV, a firstelectrical signal being an electrical command in the opening directionis input to the servo valve 23. This allows communication between theP-port and B-port of the servo valve 23, and then the control oil issupplied from the supply port 21 to the open-side channel 30 via theservo valve 23. As described above, the check valve function is lost inthe first open-side pilot check valve 33 and the second open-side pilotcheck valve 34 provided in the open-side channel 30. With thisconfiguration, the control oil supplied to the open-side channel 30 willbe supplied to the opening direction piston chamber 12.

Furthermore, the input of the first electrical signal to the servo valve23 allows the A-port and the T-port of the servo valve 23 to communicatewith each other. The closed-side pilot check valve 35 provided in thefirst closed-side channel 29 has lost the check valve function asdescribed above. With this configuration, the control oil in the closingdirection piston chamber 13 is discharged to the discharge port 22 viathe servo valve 23 and the servo discharge path 31.

When the control oil is supplied to the opening direction piston chamber12, the pressure of the control oil in the opening direction pistonchamber 12 increases. When the control oil in the closing directionpiston chamber 13 is discharged, the piston 11 is pressed by the controloil in the opening direction piston chamber 12, moving the valve body VBin the opening direction. In this manner, the steam valve SV is opened.

In contrast, in a case where the steam valve SV is rapidly closed(tripped), the trip solenoid valve 27 is de-energized as illustrated inFIG. 2, and the trip solenoid valve 27 trips due to the action of thespring. This allows communication between the B-port and T-port of thetrip solenoid valve 27 as illustrated by the broken line in FIG. 2. Thiscauses the emergency oil in the X-port of the dump valve 24 and theemergency oil in the X-port of the blocking valve 26 to be discharged tothe discharge port 22 via the emergency oil channel 46, the tripsolenoid valve 27, and the trip discharge path 47. This causes theemergency oil to be discharged from the X-port of the dump valve 24 toopen the dump valve 24, and causes the emergency oil to be dischargedfrom the X-port of the blocking valve 26 to open the blocking valve 26by the action of the spring.

In addition, de-energized of the trip solenoid valve 27 allows theemergency oil in the X-port of the first open-side pilot check valve 33,emergency oil in the X-port of the second open-side pilot check valve34, and the emergency oil in the X-port of the closed-side pilot checkvalve 35 to be discharged to the discharge port 22 in a similar manner.This causes the emergency oil to be discharged from the X-port of eachof the valves 33 to 35, allowing each of the valves 33 to 35 to exert abackflow prevention function.

Opening the dump valve 24 as described above would allow the B-port andthe A-port of the dump valve 24 to communicate with each other. Thesecond open-side pilot check valve 34 permits the flow of control oil tothe branch point P1 while the first open-side pilot check valve 33blocks the flow of control oil to the servo valve 23. Accordingly, thecontrol oil in the opening direction piston chamber 12 is discharged tothe discharge port 22 via the dump channel 40, the dump valve 24, andthe dump discharge path 41.

Moreover, opening the blocking valve 26 as described above allows theP-port and A-port of the blocking valve 26 to communicate with eachother, so as to supply the control oil in the accumulator 25 from theaccumulator discharge path 43 to the second closed-side channel 44 viathe blocking valve 26. Since the closed-side pilot check valve 35 blocksthe flow of control oil to the servo valve 23, the control oil suppliedto the second closed-side channel 44 is then supplied to the closingdirection piston chamber 13 via the first closed-side channel 29.

When the control oil is supplied to the closing direction piston chamber13, the pressure of the control oil in the closing direction pistonchamber 13 increases. When the control oil in the opening directionpiston chamber 12 is discharged, the piston 11 is pressed by the controloil in the closing direction piston chamber 13, moving the valve body VBin the closing direction. In this manner, the steam valve SV is rapidlyclosed.

When the steam valve SV is rapidly closed, the control oil in theopening direction piston chamber 12 is discharged from the dump valve 24having a large discharge capacity, making it possible to rapidlydischarge the control oil in the opening direction piston chamber 12.Furthermore, the control oil is supplied to the closing direction pistonchamber 13 from the accumulator 25 that stores the control oil underpressure. Therefore, the closing direction piston chamber 13 can berapidly supplied with the control oil. This makes it possible to rapidlyincrease the pressure of the control oil in the closing direction pistonchamber 13 for exerting the fail-safe function. This enables the valvebody VB to rapidly move in the closing direction, making it possible torapidly close the steam valve SV. That is, the fail-safe function can beenhanced.

Meanwhile, the steam valve driving apparatus 1 according to the presentembodiment is provided with the supply port-side check valve 32 providedin the first control oil supply path 28. The cracking pressure in thesupply port-side check valve 32 is set so as to correspond to theminimum operating pressure of the steam valve driving apparatus 1. Withthis configuration, even when the supply of control oil from the controloil supply system is interrupted or the supply pressure of the controloil is gradually reduced, the supply port-side check valve 32 canprevent the pressure of the control oil and the pressure of theemergency oil in the steam valve driving apparatus 1 from dropping belowthe minimum operating pressure. Furthermore, since the steam valvedriving apparatus 1 according to the present embodiment includes theaccumulator 25, the control oil can be supplied from the accumulator 25to the servo valve 23, the trip solenoid valve 27, or the like. Thisalso makes it possible to prevent the reduction of the pressure of thecontrol oil and the pressure of the emergency oil in the steam valvedriving apparatus 1. This leads to improvement of the fail-safefunction.

Furthermore, in a case where the power supply of the steam valve drivingapparatus 1 is blocked, the trip solenoid valve 27 is de-energized in asimilar manner as the case where the steam valve SV is rapidly closed.Subsequently, action of the spring allows communication between theB-port and the T-port, causing the emergency oil in the X-port of thedump valve 24 and the emergency oil in the X-port of the blocking valve26 to be discharged to the discharge port 22. This opens the dump valve24, causing the control oil in the opening direction piston chamber 12to be discharged to the discharge port 22. Moreover, the action of thespring also opens the blocking valve 26, allowing communication betweenthe P-port and the A-port of the blocking valve 26, so as to supply thecontrol oil in the accumulator 25 to the closing direction pistonchamber 13. Furthermore, the servo valve 23 is de-energized by the blockof the power supply, and the action of the spring will block the P-portand the B-port in the servo valve 23, and allows communication betweenthe P-port and the A-port. This blocks the flow of control oil towardthe opening direction piston chamber 12. This enables the steam valve SVto be rapidly closed, leading to improvement of the fail-safe function.

According to the present embodiment in this manner, in the case ofrapidly closing the steam valve SV, the dump valve 24 is controlled, bythe trip solenoid valve 27, so as to permit the flow of the control oilfrom the opening direction piston chamber 12 of the cylinder 10 to thedischarge port 22. This makes it possible to rapidly discharge thecontrol oil in the opening direction piston chamber 12 to the dischargeport 22 via the dump valve 24. Furthermore, the blocking valve 26permits the flow of control oil from the accumulator 25 to the closingdirection piston chamber 13. With this configuration, it is possible torapidly supply the control oil stored in the accumulator 25 to theclosing direction piston chamber 13, leading to a rapid increase of thepressure of the control oil in the closing direction piston chamber 13.With this configuration, the control oil in the closing direction pistonchamber 13 can press the piston 11 so as to exert the fail-safefunction, enabling the valve body VB to rapidly move in the closingdirection to rapidly close the steam valve SV.

Furthermore, according to the present embodiment, in the case of openingthe steam valve SV, the blocking valve 26 blocks the flow of control oilfrom the accumulator 25 to the closing direction piston chamber 13, andthe servo valve 23 permits the flow of control oil from the chamber 13to the discharge port 22. This makes it possible to discharge thecontrol oil in the closing direction piston chamber 13 to the dischargeport 22 via the servo valve 23. This makes it possible to prevent thepiston 11 from receiving pressure in the closing direction from thecontrol oil supplied to the closing direction piston chamber 13. As aresult, in a case where the steam valve SV is open, it is possible toprevent the force for exerting the fail-safe function from being appliedas a load to the piston 11 of the cylinder 10. In this case, it ispossible to suppress an increase in the volume of the cylinder 10,leading to miniaturization of the cylinder 10.

Furthermore, according to the present embodiment, in a case of rapidlyclosing the steam valve SV, the trip solenoid valve 27 can discharge theemergency oil in the X-port of the dump valve 24 and the emergency oilin the X-port of the blocking valve 26 to the discharge port 22. Thismakes it possible to rapidly discharge the emergency oil in the openingdirection piston chamber 12 to the discharge port 22 via the dump valve24, and at the same time, makes it possible to rapidly supply theemergency oil stored in the accumulator 25 to the closing directionpiston chamber 13. This enables rapid movement of the piston 11 in theclosing direction of the steam valve SV, and enables rapid closing ofthe steam valve SV.

Furthermore, according to the present embodiment, the first open-sidepilot check valve 33 that blocks the flow of the control oil to theservo valve 23 is provided in the open-side channel 30 connecting theservo valve 23 and the opening direction piston chamber 12, on the sidecloser to the servo valve 23 rather than to the branch point P1 to whichthe dump channel 40 is connected. This prevents the control oil frombeing supplied to the servo valve 23 when the control oil in the openingdirection piston chamber 12 is discharged to the discharge port 22.

Furthermore, according to the present embodiment, the closed-side pilotcheck valve 35 that blocks the flow of the control oil to the servovalve 23 is provided in the first closed-side channel 29 connecting theservo valve 23 and the closing direction piston chamber 13, on the sidecloser to the servo valve 23 rather than to the branch point P4 to whichthe second closed-side channel 44 is connected. This makes it possibleto prevent the control oil from being supplied to the servo valve 23 ina case where the control oil is supplied from the accumulator 25 to theclosing direction piston chamber 13.

Furthermore, according to the present embodiment, the closed-side pilotcheck valve 35 loses its backflow prevention function by supply of theemergency oil to its X-port. This makes it possible to discharge thecontrol oil in the closing direction piston chamber 13 to the dischargeport 22 via the servo valve 23 in a case where the steam valve SV isopened.

Furthermore, according to the present embodiment, the supply port-sidecheck valve 32 is provided in the first control oil supply path 28 onthe side closer to the supply port 21 rather than to the branch point P2to which the accumulator filling path 42 is connected. With thisconfiguration, the flow of control oil to the supply port 21 is blocked,making it possible to prevent the control oil and emergency oil in thesteam valve driving apparatus 1 from being supplied to the supply port21. This also makes it possible to prevent the reduction of the pressureof the control oil and the pressure of the emergency oil in the steamvalve driving apparatus 1.

The above-described embodiment has described an example in which thepiston 11 of the cylinder 10 is joined to the valve body VB of the steamvalve SV that linearly moves in the opening/closing direction. However,the present embodiment is not limited to this, and the piston 11 may bejoined to a valve body of a steam valve such as a butterfly valve thatpivots in an opening/closing direction. In this case, it is preferablethat a mechanism for converting a linear motion of the piston 11 into apivotal motion be interposed between the piston 11 and the valve body.

Moreover, the above-described embodiment is an example in which thecontrol valve indicated by reference numeral 23 is the servo valve 23.However, the present embodiment is not limited to this, and the controlvalve indicated by reference numeral 23 can also be implemented as asolenoid valve. For example, it is allowable to have a configuration inwhich energization of the coil of the solenoid valve would permit theflow of control oil from the first control oil supply path 28 to theopen-side channel 30, and de-energization of coil would block the flowof the control oil from the first control oil supply path 28 to theopen-side channel 30.

Second Embodiment

Next, a steam valve driving apparatus according to a second embodimentof the present invention will be described with reference to FIGS. 3 and4.

A main difference of the second embodiment illustrated in FIGS. 3 and 4is that the supply port-side check valve is a pilot check valvecontrolled by a trip solenoid valve. Other configuration issubstantially the same as of the first embodiment illustrated in FIGS. 1and 2. In FIGS. 3 and 4, the same portions as those of the firstembodiment illustrated in FIGS. 1 and 2 will be denoted by the samereference numerals, and a detailed description thereof will be omitted.

In the present embodiment, as illustrated in FIG. 3, the supplyport-side check valve 32 illustrated in FIGS. 1 and 2 is implemented asa pilot check valve. That is, the first control oil supply path 28 isprovided with a supply port-side pilot check valve 50 (supply port-sidebackflow prevention function valve). The supply port-side pilot checkvalve 50 is controlled by the trip solenoid valve 27.

More specifically, the A-port and the B-port of the supply port-sidepilot check valve 50 form a part of the first control oil supply path28, while the X-port of the supply port-side pilot check valve 50 isconnected to the B-port of the trip solenoid valve 27 via the emergencyoil channel 46. The supply port-side pilot check valve 50 is configuredsuch that in the state where emergency oil from the trip solenoid valve27 is supplied to the X-port, the X-port would be pressurized by theemergency oil to cause the supply port-side pilot check valve 50 to losethe backflow prevention function so as to permit the flow of control oilin both directions. In contrast, the supply port-side pilot check valve50 has a backflow prevention function in a state where emergency oil isnot supplied to the X-port. This would permit the flow of control oil tothe branch point P2, while blocking the flow of the control oil to thesupply port 21.

In the case of opening the steam valve SV, as illustrated in FIG. 3,emergency oil is supplied from the B-port of the trip solenoid valve 27to the X-port of the supply port-side pilot check valve 50, pressurizingthe X-port. Therefore, the check valve function of the supply port-sidepilot check valve 50 would be lost, permitting the flow of control oilin both directions in the supply port-side pilot check valve 50. Thisallows the control oil to be supplied from the supply port 21 to theservo valve 23, the trip solenoid valve 27, and the accumulator 25.

In the case of rapidly closing the steam valve SV, the emergency oil inthe X-port of the supply port-side pilot check valve 50 passes throughthe emergency oil channel 46, the trip solenoid valve 27, and the tripdischarge path 47 and then is discharged to the discharge port 22, asillustrated in FIG. 4. With this configuration, the emergency oil isdischarged from the X-port of the supply port-side pilot check valve 50.Therefore, the supply port-side pilot check valve 50 exerts a backflowprevention function, and this will block the flow of control oil to thesupply port 21.

Note that the accumulator 25 according to the present embodimentpreferably stores an oil amount that can pressurize the X-port so thatthe supply port-side pilot check valve 50 can lose its check valvefunction when the steam valve SV is opened after being rapidly closed.

In this manner, according to the present embodiment, the supplyport-side backflow prevention function valve is implemented as thesupply port-side pilot check valve 50. With this configuration, it ispossible to detect a decrease in the pressure of the control oil in thecontrol oil supply system, detect blocking of power supply and tripoperation of the trip solenoid valve 27, leading to prevention ofreduction in the pressure of the control oil in the steam valve drivingapparatus 1.

That is, a decrease in the pressure of the control oil in the controloil supply system leads to a decrease in the pressure of the emergencyoil in the X-port of the supply port-side pilot check valve 50. Withthis configuration, the supply port-side pilot check valve 50 can exerta backflow prevention function, making it possible to block the flow ofcontrol oil to the supply port 21. This makes it possible to prevent thecontrol oil in the steam valve driving apparatus 1 from being suppliedto the supply port 21, and prevent the reduction of the pressure of thecontrol oil in the steam valve driving apparatus 1.

Furthermore, in a case where the power supply of the steam valve drivingapparatus 1 is blocked, the trip solenoid valve 27 is de-energized. Thismakes it possible to discharge the emergency oil in the X-port of thesupply port-side pilot check valve 50. This enables the supply port-sidepilot check valve 50 to exert a backflow prevention function, and it ispossible, in a similar manner, to prevent the reduction of the pressureof the control oil in the steam valve driving apparatus 1.

Furthermore, in a case where the trip solenoid valve 27 makes tripoperation, the emergency oil in the X-port of the supply port-side pilotcheck valve 50 can be discharged. This enables the supply port-sidepilot check valve 50 to exert a backflow prevention function, and it ispossible, in a similar manner, to prevent the reduction of the pressureof the control oil in the steam valve driving apparatus 1.

Third Embodiment

Next, a steam valve driving apparatus according to a third embodiment ofthe present invention will be described with reference to FIGS. 5 and 6.

A main difference of the third embodiment illustrated in FIGS. 5 and 6is that the supply port-side check valve is a solenoid valve. Otherconfiguration is substantially the same as of the first embodimentillustrated in FIGS. 1 and 2. In FIGS. 5 and 6, the same portions asthose of the first embodiment illustrated in FIGS. 1 and 2 will bedenoted by the same reference numerals, and a detailed descriptionthereof will be omitted.

In the present embodiment, as illustrated in FIG. 5, the supplyport-side check valve 32 illustrated in FIGS. 1 and 2 is implemented asa solenoid valve. That is, the first control oil supply path 28 isprovided with a supply port-side solenoid valve 51 (supply port-sidebackflow prevention function valve).

Similarly to the servo valve 23 and the trip solenoid valve 27, thesupply port-side solenoid valve 51 includes a coil that is energizedwhen it receives an electrical signal transmitted from a control device(not illustrated). The supply port-side solenoid valve 51 has aconfiguration in which, in a state where the coil is energized, theP-port and B-port of the supply port-side solenoid valve 51 communicateswith each other, losing the backflow prevention function so as to permitthe flow of control oil in both directions. In contrast, the supplyport-side solenoid valve 51 has a backflow prevention function obtainedby the action of a spring, and blocks the flow of control oil to thesupply port 21 in a state where the coil is de-energized. In the presentembodiment, the flow of control oil to the branch point P2 is alsoblocked in a de-energized state.

In the case of opening the steam valve SV, the supply port-side solenoidvalve 51 is energized as illustrated in FIG. 5. Therefore, the backflowprevention function of the supply port-side solenoid valve 51 would belost, permitting the flow of control oil in both directions in thesupply port-side solenoid valve 51. This allows the control oil to besupplied from the supply port 21 to the servo valve 23, the tripsolenoid valve 27, and the accumulator 25.

In the case of rapidly closing the steam valve SV, the supply port-sidesolenoid valve 51 will be de-energized as illustrated in FIG. 6.Therefore, the supply port-side solenoid valve 51 exerts a backflowprevention function, and this blocks the flow of control oil to thesupply port 21.

In this manner, according to the present embodiment, the supplyport-side backflow prevention function valve is implemented as thesupply port-side solenoid valve 51. With this configuration, it ispossible to detect a decrease in the pressure of the control oil in thecontrol oil supply system, detect blocking of power supply, leading toprevention of reduction in the pressure of the control oil and pressureof the emergency oil in the steam valve driving apparatus 1.

That is, in a case where the pressure of the control oil in the controloil supply system decreases, the supply port-side solenoid valve 51 canbe controlled to perform de-energization. This enables the supplyport-side solenoid valve 51 to exert a backflow prevention function,making it possible to block the flow of control oil to the supply port21. This makes it possible to prevent the control oil and the emergencyoil in the steam valve driving apparatus 1 from being supplied to thesupply port 21, and prevent the reduction of the pressure of the controloil and the pressure of the emergency oil in the steam valve drivingapparatus 1.

Furthermore, in a case where the power supply of the steam valve drivingapparatus 1 is blocked, the supply port-side solenoid valve 51 isde-energized. This enables the supply port-side solenoid valve 51 toexert a backflow prevention function, and it is possible, in a similarmanner, to prevent the reduction of the pressure of the control oil andthe pressure of the emergency oil in the steam valve driving apparatus1.

The above-described embodiment has described an example in which thesupply port-side solenoid valve 51 is implemented as a spool valve.However, the present embodiment is not limited to this, and the supplyport-side solenoid valve 51 may be implemented as a poppet valve. Forexample, the supply port-side solenoid valve 51 may be configured to beenergized and opened in the case of opening the steam valve SV (FIG. 5),and be de-energized and closed in the case of rapidly closing the steamvalve SV (FIG. 6). In this case, it is possible to further prevent thereduction of the pressure of the control oil and the pressure of theemergency oil in the steam valve driving apparatus 1.

Fourth Embodiment

Next, a steam valve driving apparatus according to a fourth embodimentof the present invention will be described with reference to FIGS. 7 and8.

A main difference of the fourth embodiment illustrated in FIGS. 7 and 8is that hydraulic oil is supplied to the accumulator via the tripsolenoid valve. Other configuration is substantially the same as of thefirst embodiment illustrated in FIGS. 1 and 2. In FIGS. 7 and 8, thesame portions as those of the first embodiment illustrated in FIGS. 1and 2 will be denoted by the same reference numerals, and a detaileddescription thereof will be omitted.

In the present embodiment, as illustrated in FIG. 7, the B-port of tripsolenoid valve 27 and accumulator 25 are connected by the accumulatorfilling path 42. That is, the accumulator filling path 42 according tothe present embodiment is connected to the emergency oil channel 46 asillustrated in FIG. 7, rather than connected to the first control oilsupply path 28 as illustrated in FIG. 1. The control oil supplied to thetrip solenoid valve 27 is supplied to the accumulator 25 via theemergency oil channel 46 and the accumulator filling path 42, and theaccumulator 25 is filled with the control oil.

The accumulator filling path 42 is provided with an accumulator-sidecheck valve 52 (accumulator-side backflow prevention valve). Thisaccumulator-side check valve 52 is configured to permit the flow to theaccumulator 25 and block the flow to the trip solenoid valve 27 (morespecifically, the emergency oil channel 46). In addition, the crackingpressure of the accumulator-side check valve 52 is set to a minimumoperating pressure of the steam valve driving apparatus 1.

In a case where the steam valve SV is opened, the control oil issupplied from the B-port of the trip solenoid valve 27 to theaccumulator 25 via the accumulator filling path 42, as illustrated inFIG. 7.

In the case of rapidly closing the steam valve SV, as illustrated inFIG. 8, the blocking valve 26 is opened. Subsequently, the control oilin the accumulator 25 is supplied from the accumulator discharge path 43to the closing direction piston chamber 13 via the blocking valve 26,the second closed-side channel 44, and the first closed-side channel 29.At this time, the emergency oil is discharged from the emergency oilchannel 46. Since the accumulator-side check valve 52 is provided in theaccumulator filling path 42, it is possible to prevent the control oilin the accumulator 25 from flowing from the accumulator filling path 42to the emergency oil channel 46.

In this manner, according to the present embodiment, theaccumulator-side check valve 52 is provided in the accumulator fillingpath 42 that connects the accumulator 25 to the trip solenoid valve 27.With this configuration, the control oil stored in the accumulator 25can be supplied to the blocking valve 26. This makes it possible toprevent the control oil stored in the accumulator 25 from being suppliedto the servo valve 23 and the trip solenoid valve 27. Accordingly, thecontrol oil in the accumulator 25 can be used for operation for rapidlyclosing the steam valve SV, leading to improvement of the reliability ofthe steam valve driving apparatus 1.

Fifth Embodiment

Next, a steam valve driving apparatus according to a fifth embodiment ofthe present invention will be described with reference to FIGS. 9 and10.

A main difference of the fifth embodiment illustrated in FIGS. 9 and 10is that the accumulator-side check valve is a pilot check valvecontrolled by a trip solenoid valve. Other configuration issubstantially the same as of the fourth embodiment illustrated in FIGS.7 and 8. In FIGS. 9 and 10, the same portions as those of the fourthembodiment illustrated in FIGS. 7 and 8 will be denoted by the samereference numerals, and a detailed description thereof will be omitted.

In the present embodiment, as illustrated in FIG. 9, theaccumulator-side check valve illustrated in FIGS. 7 and 8 is implementedas a pilot check valve. That is, the accumulator filling path 42 isprovided with an accumulator-side pilot check valve 53 (accumulator-sidebackflow prevention valve). This accumulator-side pilot check valve 53is controlled by a trip solenoid valve 27.

More specifically, the A-port and the B-port of the accumulator-sidepilot check valve 53 form a part of the accumulator filling path 42. TheB-port of trip solenoid valve 27 is connected to the X-port of theaccumulator-side pilot check valve 53 via the emergency oil channel 46.The accumulator-side pilot check valve 53 is configured such that in astate where emergency oil from the trip solenoid valve 27 is supplied tothe X-port, the X-port would be pressurized by the emergency oil. Thiswill cause the accumulator-side pilot check valve 53 to lose thebackflow prevention function, and permit the flow of control oil in bothdirections. In contrast, the accumulator-side pilot check valve 53 has abackflow prevention function in a state where the emergency oil is notsupplied to the X-port. This would permit the flow of control oil to theaccumulator 25, while blocking the flow of the control oil to the tripsolenoid valve 27 (more specifically, the emergency oil channel 46).

In the case of opening the steam valve SV, as illustrated in FIG. 9,emergency oil is supplied from the B-port of the trip solenoid valve 27to the X-port of the accumulator-side pilot check valve 53, pressurizingthe X-port. Therefore, the check valve function of the accumulator-sidepilot check valve 53 would be lost, permitting the flow of control oilin both directions in the accumulator-side pilot check valve 53. Thisallows the control oil to be supplied from the trip solenoid valve 27 tothe accumulator 25.

In the case of rapidly closing the steam valve SV, the emergency oil inthe X-port of the accumulator-side pilot check valve 53 is discharged tothe discharge port 22 via the emergency oil channel 46, the tripsolenoid valve 27, and the trip discharge path 47, as illustrated inFIG. 10. With this configuration, the emergency oil is discharged fromthe X-port of the accumulator-side pilot check valve 53. Therefore, theaccumulator-side pilot check valve 53 exerts a backflow preventionfunction, and this will block the flow of control oil to the emergencyoil channel 46.

In this manner, according to the present embodiment, theaccumulator-side pilot check valve 53 is provided in the accumulatorfilling path 42 that connects the accumulator 25 to the trip solenoidvalve 27. With this configuration, the control oil stored in theaccumulator 25 can be supplied to the blocking valve 26. This makes itpossible to prevent the control oil stored in the accumulator 25 frombeing supplied to the servo valve 23 and the trip solenoid valve 27.Accordingly, the control oil in the accumulator 25 can be used foroperation for rapidly closing the steam valve SV, leading to improvementof the reliability of the steam valve driving apparatus 1.

Sixth Embodiment

Next, a steam valve driving apparatus according to a sixth embodiment ofthe present invention will be described with reference to FIGS. 11 and12.

A main difference of the sixth embodiment illustrated in FIGS. 11 and 12is in that a second piston releasably provided with respect to the firstpiston of the cylinder is pressed in the closing direction of the valvebody by the closing spring. Other configurations are substantially thesame as those of the first embodiment illustrated in FIGS. 1 and 2. InFIGS. 11 and 12, the same portions as those of the first embodimentillustrated in FIGS. 1 and 2 will be denoted by the same referencenumerals, and a detailed description thereof will be omitted.

In the present embodiment, as illustrated in FIG. 11, the cylinder 10includes a first piston 11 (corresponding to the piston 11 illustratedin FIG. 1) joined to the valve body VB, an opening direction firstpiston chamber (corresponding to the opening direction piston chamber 12illustrated in FIG. 1) and a closing direction first piston chamber(corresponding to the closing direction piston chamber 13 illustrated inFIG. 1). The cylinder 10 further includes a second piston 60 releasablyprovided with respect to the valve body VB of the steam valve SV, anopening direction second piston chamber 61, and a closing directionsecond piston chamber 62.

In the present embodiment, the first piston 11 is joined to the valvebody VB, and the second piston 60 is releasably provided with respect tothe first piston 11. More specifically, a first coupling member 63 isprovided at the second piston 60-side end of the first piston 11, and asecond coupling member 64 is provided at the first piston 11-side end ofthe second piston 60. In a case where the steam valve SV is closed, thesecond coupling member 64 comes in contact with the first couplingmember 63, causing the second piston 60 to be joined to the valve bodyVB via the first piston 11. The second piston 60 is configured to pressthe first piston 11 to a fully closed position of the steam valve SV. Incontrast, in a case where the steam valve SV is opened, the secondcoupling member 64 is separated from the first coupling member 63,causing the second piston 60 to be separated from the first piston 11(that is, the valve body VB). Note that while the first coupling member63 and the second coupling member 64 are drawn so as to be engaged witheach other in FIG. 11 or the like, facing surfaces of individual membersmay have flat shapes.

The opening direction second piston chamber 61 is configured to besupplied with control oil that presses the second piston 60 in theopening direction of the valve body VB.

The closing direction second piston chamber 62 is configured to pressthe second piston 60 in the closing direction of the valve body VB. Morespecifically, the closing direction second piston chamber 62 is providedwith a closing spring 65 that presses the second piston 60 in theclosing direction of the valve body VB. The second piston 60 is pressedby the biasing force of the closing spring 65 in the closing directionof the valve body VB.

The manifold block 20 in the present embodiment includes the servo valve23, a first dump valve (corresponding to the dump valve 24 illustratedin FIG. 1), the trip solenoid valve 27, and a second dump valve 66. Theaccumulator 25 or the blocking valve 26 as illustrated in FIG. 1 or thelike, or the supply port-side backflow prevention function valve (supplyport-side check valve 32 illustrated in FIG. 1, supply port-side pilotcheck valve 50 illustrated in FIG. 3, or the supply port-side solenoidvalve 51 illustrated in FIG. 5) is not provided.

The control oil in the opening direction first piston chamber 12 is tobe discharged via the first dump valve 24.

The control oil in the opening direction second piston chamber 61 is tobe discharged via the second dump valve 66. The second dump valve 66 isconfigured to be switchable between a state blocking the flow of controloil from the opening direction second piston chamber 61 to the dischargeport 22 and a state permitting the flow of control oil (to permit orblock the flow of the control oil).

More specifically, the second dump valve 66 has a configuration in whichthe B-port of the second dump valve 66 and the opening direction secondpiston chamber 61 are connected by the second dump channel 67. TheA-port of the second dump valve 66 is connected with the second dumpdischarge path 68. The second dump discharge path 68 is connected to thedischarge port 22 via a first dump discharge path (corresponding to thedump discharge path 41 illustrated in FIG. 1). The X-port (pilot port)of the second dump valve 66 is connected to the B-port of the tripsolenoid valve 27.

The second dump valve 66 is controlled by the trip solenoid valve 27.That is, the second dump valve 66 is configured such that, in a statewhere emergency oil is supplied from the B-port to the X-port of thetrip solenoid valve 27, the X-port is pressurized by the emergency oiland closed, blocking the B-port and the A-port of the second dump valve66. This blocks the flow of control oil from the opening directionsecond piston chamber 61 to the discharge port 22. In contrast, in astate where the emergency oil is not supplied to the X-port, the seconddump valve 66 is opened, allowing communication between the B-port andthe A-port of the second dump valve 66. This permits the flow of controloil from the opening direction second piston chamber 61 to the dischargeport 22, allowing the control oil to be supplied from the openingdirection second piston chamber 61 to the second dump discharge path 68via the B-port and the A-port of the second dump valve 66. The controloil supplied to the second dump discharge path 68 is then supplied tothe discharge port 22 via the first dump discharge path 41 anddischarged from the discharge port 22.

The trip discharge path 47 is provided with a second check valve 69. Thesecond check valve 69 is disposed in the trip discharge path 47 on theside closer to the trip solenoid valve 27 rather than to the branchpoint P5 to which the second dump discharge path 68 is connected. Thesecond check valve 69 is configured to permit the flow of the emergencyoil to the branch point P5 and block the flow of the control oil to thetrip solenoid valve 27. That is, the second check valve 69 prevents thecontrol oil discharged from the second dump valve 66 from being suppliedto the T-port of the trip solenoid valve 27.

In a case where the steam valve SV is opened, as illustrated in FIG. 11,the first electrical signal that is an opening direction electricalcommand is input to the servo valve 23, and then the control oils issupplied from the supply port 21 to the opening direction first pistonchamber 12 via the servo valve 23. The first dump valve 24 is closedbecause emergency oil is supplied from the trip solenoid valve 27 to thefirst dump valve 24. Furthermore, the trip solenoid valve 27 isenergized, and the control oil (or emergency oil) is supplied from thesupply port 21 to the opening direction second piston chamber 61 via thetrip solenoid valve 27. On the other hand, an input of the firstelectrical signal to the servo valve 23 causes the control oil in theclosing direction first piston chamber 13 to be discharged from thedischarge port 22 via the servo valve 23.

When the control oil is supplied to the opening direction second pistonchamber 61, the pressure of the control oil in the opening directionsecond piston chamber 61 increases. With this configuration, thepressure of the control oil in the opening direction second pistonchamber 61 presses the second coupling member 64 of the second piston 60in the opening direction of the valve body VB. Resisting the biasingforce of the closing spring 65, the second coupling member 64 isseparated from the first coupling member 63 of the first piston 11. Forthis reason, while the steam valve SV is open, the second piston 60 isseparated from the first piston 11, and the biasing force of the closingspring 65 is not applied as a load to the first piston 11.

When the control oil is supplied to the opening direction first pistonchamber 12, the pressure of the control oil in the opening directionfirst piston chamber 12 increases. When the control oil in the closingdirection first piston chamber 13 is discharged, the first piston 11 ispressed in the opening direction of the valve body VB by the pressure ofthe control oil in the opening direction first piston chamber 12, movingthe valve body VB in the opening direction. In this manner, the steamvalve SV is opened.

In contrast, in a case where the steam valve SV is rapidly closed, thetrip solenoid valve 27 trips as illustrated in FIG. 12. Subsequently,the emergency oil in the X-port of the first dump valve 24 and theemergency oil in the X-port of the second dump valve 66 are discharged,and the first dump valve 24 and the second dump valve 66 will each beopened. Therefore, the control oil in the opening direction first pistonchamber 12 is discharged to the discharge port 22 via the first dumpdischarge path 41. The control oil in the opening direction secondpiston chamber 61 is discharged to the discharge port 22 via the seconddump discharge path 68 and the first dump discharge path 41.

When the control oil in the opening direction second piston chamber 61is discharged, the second piston 60 moves in the closing direction ofthe valve body VB by the biasing force of the closing spring 65, and thesecond coupling member 64 of the second piston comes into contact withthe first coupling member 63 of the first piston 11. With thisconfiguration, the biasing force of the closing spring 65 is applied asa load to the first piston 11 via the second piston 60, and the firstpiston 11 moves together with the second piston 60 in the closingdirection of the valve body VB. In the present embodiment, the controloil is supplied to the closing direction first piston chamber 13 via theservo valve 23. With this configuration, the first piston 11 is pressedin the closing direction of the valve body VB by the pressure of thecontrol oil supplied to the closing direction first piston chamber 13,making it possible to increase the force for moving the valve body VB inthe closing direction.

In this manner, the valve body VB moves in the closing direction, andthe steam valve SV is closed rapidly. At this time, the control oil inthe opening direction first piston chamber 12 is discharged from thefirst dump valve 24 having a large discharge capacity, and together withthis, the control oil in the opening direction second piston chamber 61is discharged from the second dump valve 66 having a large dischargecapacity. Accordingly, it is possible to rapidly discharge each of thecontrol oil in the opening direction first piston chamber 12 and thecontrol oil in the opening direction second piston chamber 61.Furthermore, since the closing direction second piston chamber 62 isprovided with the closing spring 65, it is possible to rapidly apply, asa load, the biasing force of the closing spring 65 for exerting thefail-safe function to the first piston 11 and the second piston 60. Thisenables the valve body VB to rapidly move in the closing direction,making it possible to rapidly close the steam valve SV. That is, thefail-safe function can be enhanced.

Moreover, in a case where the power supply of the steam valve drivingapparatus 1 is blocked, the trip solenoid valve 27 is de-energized, andthe second electrical signal that is an electrical command in theclosing direction is input to the servo valve 23. This enables the steamvalve SV to be rapidly closed as described above, leading to improvementof the fail-safe function.

In this manner, according to the present embodiment, in the case ofrapidly closing the steam valve SV, it is possible to rapidly dischargethe control oil in the opening direction first piston chamber 12 to thedischarge port 22 via the first dump valve 24. Furthermore, it is alsopossible to rapidly discharge the control oil in the opening directionsecond piston chamber 61 to the discharge port 22 via the second dumpvalve 66. In contrast, since the closing spring 65 is provided in theclosing direction second piston chamber 62, the closing spring 65 canpress the first piston 11 and the second piston 60 so as to exert afail-safe function. This makes it possible to rapidly close the steamvalve SV by rapidly moving the valve body VB in the closing direction.In contrast, in the case of opening the steam valve SV, it is possibleto supply the control oil from the trip solenoid valve 27 to the openingdirection second piston chamber 61, enabling an increase in the pressureof the control oil in the opening direction second piston chamber 61.With this configuration, the second piston 60 will be pressed in theopening direction of the valve body VB by the control oil in the openingdirection second piston chamber 61, enabling the second piston 60 to beseparated from the first piston 11. For this reason, it is possible toprevent the biasing force of the closing spring 65 from being applied asa load to the first piston 11. As a result, in cases other than the casewhere the steam valve SV is to be rapidly closed, it is possible toprevent the force for exerting the fail-safe function from being appliedas a load to the first piston 11. In this case, it is possible tosuppress an increase in the volume of the cylinder 10, leading tominiaturization of the cylinder.

Furthermore, according to the present embodiment, it is possible torapidly close the steam valve SV by the biasing force of the closingspring 65 even when the emergency oil is lost. This makes it possible tofurther enhance the reliability of the steam valve driving apparatus 1.

Seventh Embodiment

Next, a steam valve driving apparatus according to a seventh embodimentof the present invention will be described with reference to FIGS. 13and 14.

A main difference of the seventh embodiment illustrated in FIGS. 13 and14 is that the second piston is joined to the valve body via the joiningmember not via the first piston in a case where the second piston closesthe steam valve. Other configurations are substantially the same asthose of the sixth embodiment illustrated in FIGS. 11 and 12. In FIGS.13 and 14, the same portions as those of the sixth embodimentillustrated in FIGS. 11 and 12 will be denoted by the same referencenumerals, and a detailed description thereof will be omitted.

In the present embodiment, as illustrated in FIGS. 13 and 14, in thecase of rapidly closing the steam valve SV, the second piston 60 isjoined to the valve body VB via a joining member 70, not via the firstpiston 11. More specifically, as illustrated in FIG. 14, in the case ofrapidly closing the steam valve SV, the second coupling member 64 of thesecond piston 60 is configured to come in contact with the joiningmember 70 joined to the valve body VB (more specifically, come incontact with a third coupling member 71 provided at a second piston60-side end of the joining member 70), and thus, the second couplingmember 64 is to be joined to the valve body VB (or valve rod VA) via thejoining member 70. In contrast, as illustrated in FIG. 13, in the caseof opening the steam valve SV, the second coupling member 64 isseparated from the third coupling member 71, causing the second piston60 to be separated from the joining member 70 (that is, the valve bodyVB).

In this manner, according to the present embodiment, the second piston60 is to be joined to the joining member 70 joined to the valve body VB,rather than to the first piston 11, in the case of rapidly closing thesteam valve SV. This makes it possible to directly transmit the biasingforce of the closing spring 65 to the valve body VB. This enablesfurther rapid movement of the valve body VB in the closing direction,enabling the steam valve SV to be closed further rapidly.

Eighth Embodiment

Next, a steam valve driving apparatus according to an eighth embodimentof the present invention will be described with reference to FIGS. 15and 16.

A main difference of the eighth embodiment illustrated in FIGS. 15 and16 is that the steam that presses the second piston in the closingdirection of the valve body is supplied to the closing direction secondpiston chamber. Other configurations are substantially the same as thosein the sixth embodiment illustrated in FIGS. 11 and 12. In FIGS. 15 and16, the same portions as those of the sixth embodiment illustrated inFIGS. 11 and 12 will be denoted by the same reference numerals, and adetailed description thereof will be omitted.

In the present embodiment, as illustrated in FIGS. 15 and 16, steam forpressing the second piston 60 in the closing direction of the valve bodyVB is supplied to the closing direction second piston chamber 62. Morespecifically, the closing direction second piston chamber 62 isconnected to a steam extraction pipe 73 branched from a steam pipe 72that supplies steam to the steam valve SV. With this configuration, theclosing direction second piston chamber 62 is filled with steam, and thepressure in the closing direction second piston chamber 62 increases tothe pressure of the steam in the steam pipe 72. With this pressure, thesecond piston 60 is pressed in the closing direction of the valve bodyVB. In the present embodiment, the closing direction second pistonchamber 62 is not provided with a closing spring 65 that is illustratedin FIG. 11. As illustrated in FIG. 16, in the case of rapidly closingthe steam valve SV, the second piston 60 moves in the closing directiondue to the pressure of the steam, the second coupling member 64 comes incontact with the first coupling member 63, causing the second piston 60to be joined to the valve body VB via the first piston 11. In contrast,as illustrated in FIG. 15, in the case of opening the steam valve SV,the second piston 60 moves in the opening direction by the pressure ofthe control oil supplied to the opening direction second piston chamber61, and the second coupling member 64 is separated from the firstcoupling member 63, causing the second piston 60 to be separated fromthe first piston 11.

In this manner, in the present embodiment, the steam for pressing thesecond piston 60 in the closing direction of the valve body VB issupplied to the closing direction second piston chamber 62. This makesit possible to obtain the force for exerting the fail-safe function fromthe steam, leading to a simplified configuration of the steam valvedriving apparatus 1.

The above embodiment has described an example in which the second piston60 is joined to the valve body VB via the first piston 11 in the case ofrapidly closing the steam valve SV. However, the present embodiment isnot limited to this. The second piston 60 may be joined to the valvebody VB not via the first piston 11 in the case of rapidly closing thesteam valve SV, as in the configuration illustrated in FIGS. 13 and 14.

Ninth Embodiment

Next, a steam valve driving apparatus according to a ninth embodiment ofthe present invention will be described with reference to FIGS. 17 to20.

A main difference of the ninth embodiment illustrated in FIGS. 17 to 20is that the second piston is provided with a weight member that pressesthe second piston in the closing direction of the valve body. Otherconfigurations are substantially the same as those in the sixthembodiment illustrated in FIGS. 11 and 12. In FIGS. 17 to 20, the sameportions as those of the sixth embodiment illustrated in FIGS. 11 and 12will be denoted by the same reference numerals, and a detaileddescription thereof will be omitted.

In the present embodiment, as illustrated in FIGS. 17 and 18, the secondpiston 60 is provided with a weight member 74 that presses the secondpiston 60 in the closing direction of the valve body VB. The weightmember 74 preferably has a mass that can rapidly close the valve body VBof the steam valve SV. In the present embodiment, the closing directionsecond piston chamber 62 is not provided with a closing spring 65 thatis illustrated in FIG. 11. As illustrated in FIG. 18, in the case ofrapidly closing the steam valve SV, the second piston 60 moves in theclosing direction due to the weight of the weight member 74, the secondcoupling member 64 comes in contact with the first coupling member 63,causing the second piston 60 to be joined to the valve body VB via thefirst piston 11. In contrast, as illustrated in FIG. 17, in the case ofopening the steam valve SV, the second piston 60 moves in the openingdirection by the pressure of the control oil supplied to the openingdirection second piston chamber 61, and the second coupling member 64 isseparated from the first coupling member 63, causing the second piston60 to be separated from the first piston 11.

In this manner, according to the present embodiment, the second piston60 is provided with the weight member 74 that presses the second piston60 in the closing direction of the valve body VB. This makes it possibleto obtain the force for exerting the fail-safe function from the weightmember 74, leading to a simplified configuration of the steam valvedriving apparatus 1.

The above embodiment has described an example in which the second piston60 is joined to the valve body VB via the first piston 11 in the case ofrapidly closing the steam valve SV. However, the present embodiment isnot limited to this. The second piston 60 may be joined to the valvebody VB via the joining member 70, not via the first piston 11, in thecase of rapidly closing the steam valve SV, as in the configurationillustrated in FIGS. 13 and 14. More specifically, as illustrated inFIG. 20, in the case of rapidly closing the steam valve SV, it isallowable to configure such that the second coupling member 64 of thesecond piston 60 comes in contact with the third coupling member 71 ofthe joining member 70 joined to the valve body VB, and that the secondpiston 60 is joined to the valve body VB via the joining member 70. Incontrast, as illustrated in FIG. 19, it is allowable to have aconfiguration in which, in the case of opening the steam valve SV, thesecond coupling member 64 is separated from the third coupling member71, causing the second piston 60 to be separated from the joining member70. In the configuration illustrated in FIGS. 19 and 20, the gravity ofthe weight member 74 can be directly transmitted to the valve body VB.This enables further rapid movement of the valve body VB in the closingdirection, enabling the steam valve SV to be closed further rapidly.

According to the embodiment described above, it is possible to preventthe force for exerting the fail-safe function from being applied as aload to the piston of the cylinder in a case where the steam valve isopen.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions. Further, it will be understood that theseembodiments can be at least partially combined properly withoutdeparting from the spirit of the present invention.

The invention claimed is:
 1. A steam valve driving apparatus regulatingopen and close position of a steam valve, comprising: a supply portconfigured to supply hydraulic oil; a discharge port configured todischarge the hydraulic oil; a cylinder including a piston joined to thesteam valve, an opening direction piston chamber to which the hydraulicoil for pressing the piston in an opening direction of the steam valveis supplied, and a closing direction piston chamber to which thehydraulic oil for pressing the piston in a closing direction of thesteam valve is supplied; a control valve configured to permit or block aflow of the hydraulic oil from the supply port to the opening directionpiston chamber; a dump valve configured to block or permit a flow of thehydraulic oil from the opening direction piston chamber to the dischargeport; an accumulator configured to store the hydraulic oil underpressure; a blocking valve configured to permit or block a flow of thehydraulic oil from the accumulator to the closing direction pistonchamber; and a trip solenoid valve configured to control the dump valveand the blocking valve, wherein the control valve configured to permit aflow of a control oil from the closing direction piston chamber to thedischarge port in the permission of the hydraulic oil from the supplyport to the opening direction piston chamber.
 2. The steam valve drivingapparatus according to claim 1, wherein the trip solenoid valve isswitchable between a state in which the flow of the hydraulic oil fromthe opening direction piston chamber to the discharge port is blocked,and the flow of the hydraulic oil from the accumulator to the closingdirection piston chamber is blocked, when the flow of the hydraulic oilis permitted from the supply port to a pilot port of the dump valve andto a pilot port of the blocking valve, and a state in which the flow ofthe hydraulic oil from the opening direction piston chamber to thedischarge port is permitted, and that the flow of the hydraulic oil fromthe accumulator to the closing direction piston chamber is permitted,when the flow of the hydraulic oil is permitted from the pilot port ofthe dump valve and the pilot port of the blocking valve to the dischargeport.
 3. The steam valve driving apparatus according to claim 1, furthercomprising: an open-side channel connecting the control valve and theopening direction piston chamber; an open-side backflow prevention valvearranged in the open-side channel; and a dump channel connecting thedump valve with a halfway position arranged in the open-side channel onthe side closer to the opening direction piston chamber rather than tothe open-side backflow prevention valve, wherein the open-side backflowprevention valve blocks the flow of the hydraulic oil to the controlvalve.
 4. The steam valve driving apparatus according to claim 1,further comprising: a first closed-side channel connecting the controlvalve and the closing direction piston chamber; a second closed-sidechannel connecting the halfway position of the first closed-side channeland the blocking valve; and a closed-side backflow prevention valvearranged in the first closed-side channel on the side closer to thecontrol valve rather than to the halfway position at which the secondclosed-side channel is connected, wherein the closed-side backflowprevention valve blocks the flow of the hydraulic oil to the controlvalve.
 5. The steam valve driving apparatus according to claim 4,wherein the closed-side backflow prevention valve is a pilot check valvecontrolled by the trip solenoid valve.
 6. The steam valve drivingapparatus according to claim 1, further comprising: a hydraulic oilsupply path connecting the supply port and the control valve; anaccumulator filling path that connects the halfway position of thehydraulic oil supply path and the accumulator, and that supplies thehydraulic oil to the accumulator; and a supply port-side backflowprevention function valve that is arranged in the hydraulic oil supplychannel on the side closer to the supply port rather than to the halfwayposition at which the accumulator filling path is connected, and thatblocks the flow of the hydraulic oil to the supply port.
 7. The steamvalve driving apparatus according to claim 6, wherein the supplyport-side backflow prevention function valve is a pilot check valvecontrolled by the trip solenoid valve.
 8. The steam valve drivingapparatus according to claim 6, wherein the supply port-side backflowprevention function valve is a solenoid valve.
 9. The steam valvedriving apparatus according to claim 1, further comprising: anaccumulator filling path that connects the trip solenoid valve and theaccumulator, and that supplies the hydraulic oil from the trip solenoidvalve to the accumulator; and an accumulator-side backflow preventionvalve that is arranged in the accumulator filling path and that blocksthe flow of the hydraulic oil to the trip solenoid valve.
 10. The steamvalve driving apparatus according to claim 9, wherein theaccumulator-side backflow prevention valve is a pilot check valvecontrolled by the trip solenoid valve.
 11. A steam valve drivingapparatus regulating open and close position of a steam valve,comprising: a supply port configured to supply hydraulic oil; adischarge port configured to discharge the hydraulic oil; a cylinderincluding a first piston joined to the steam valve, an opening directionfirst piston chamber to which the hydraulic oil that presses the firstpiston in an opening direction of the steam valve is supplied, and asecond piston releasably arranged with respect to the steam valve, anopening direction second piston chamber to which the hydraulic oil thatpresses the second piston in the opening direction of the steam valve issupplied, and a closing direction second piston chamber that presses thesecond piston in a closing direction of the steam valve; a control valveconfigured to permit or block a flow of the hydraulic oil from thesupply port to the opening direction first piston chamber; a first dumpvalve configured to block or permit a flow of the hydraulic oil from theopening direction first piston chamber to the discharge port; a tripsolenoid valve configured to permit or block a flow of the hydraulic oilfrom the supply port to the opening direction second piston chamber; anda second dump valve configured to block or permit a flow of thehydraulic oil from the opening direction second piston chamber to thedischarge port, wherein the second piston is joined to the steam valvein a case of closing the steam valve, and is separated from the steamvalve in a case of opening the steam valve.
 12. The steam valve drivingapparatus according to claim 11, wherein the second piston is joined tothe steam valve via the first piston in the case of closing the steamvalve.
 13. The steam valve driving apparatus according to claim 11,further comprising a joining member joined to the steam valve, whereinthe second piston is joined to the steam valve via the joining member,not via the first piston, in the case of closing the steam valve. 14.The steam valve driving apparatus according to claim 11, wherein theclosing direction second piston chamber is arranged with a closingspring that presses the second piston in the closing direction of thesteam valve.
 15. The steam valve driving apparatus according to claim11, wherein steam that presses the second piston in the closingdirection of the steam valve is supplied to the closing direction secondpiston chamber.
 16. The steam valve driving apparatus according to claim11, wherein the second piston is arranged with a weight member thatpresses the second piston in the closing direction of the steam valve.